UC-NRLF 


DAIRY  LABORATORY 
1       GUIDE 


H.E.  ROSS 


GIFT   OF 
Agricultural  Educ.Div. 


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A  DAIRY 

LABORATORY 

GUIDE 


By 
H.  E.  ROSS 

\' 
Assistant  Professor  of  Dairy  Industry 

New  York  State  College  of  Agriculture  at  Cornell  University 


NEW  YORK 

ORANGE    JUDD     COMPANY 

1912 


SP253 


MAIM 


C 


Copyright,  1910,  by 

ORANGE  JUDD  COMPANY 

All  Rights  Reserved 


•  ••     •  •      ••»,••• 


Prtnted  in  M*  C7. 


PREFACE 

In  the  study  of  any  science  the  student  should, 
so  far  as  possible,  work  out  his  own  problems.  Yet 
the  beginner  may  be  saved  much  useless  time  and 
labor  by  helpful  suggestions  at  the  proper  time. 
This  Manual  is  designed  as  a  guide  to  students  in 
dairy  laboratory  work,  with  just  enough  explana- 
tion given  to  supplement  the  exercises  which  are 
outlined  in  the  Manual.  It  is  not  intended  for  a 
text  book  and  should  not  be  used  in  the  place  of 
one. 

The  author's  thanks  are  due  Prof.  W.  A.  Stock- 
ing, Jr.,  for  many  helpful  suggestions  in  the  ar- 
rangement and  preparation  of  this  book. 

The  author  recognizes  that  a  book  of  this  kind 
needs  frequent  revision,  and  an  effort  will  be  made 
to  keep  this  Manual  up  to  date. 

H.  E.  Ross. 
Dairy  Laboratories, 
New  York  State  College  of  Agriculture, 
at  Cornell  Uuiversity. 

August  31,  1910. 


ill 


TABLE   OF   CONTENTS 


I 
The  Composition  of  Milk I 

II 
Explanation.     The  Babcock  Test 5 

III 

Explanation  of  Boiled  Milk  Test  and  Formalde- 
hyde Test  18 

IV 

Explanation.     Mixing   Samples   of   Butter   Be- 
fore Testing-  for  Fat  and  Moisture 19 

V 

Explanation.    The  C.  U.  Butter  Moisture  Test     23 

VI 

Explanation.     The  Specific  Gravity  of  Milk  and 

the  Lactometer  27 

VII 

Explanation.    The  Board  of  Health  Lactometer    37 


VI  DAIRY   LABORATORY   GUIDE 

VIII 

Explanation.     Use    of   the    Hand    Machine    in 

Babcock  Test 38 

IX 
Explanation.     The  Acidity  of  Milk 43 

X 

Explanation.     The  Effect  of  Speed  of  Machine 

on  the  Babcock  Test 51 

XI 
Explanation.      Commercial  Rennet  and  Its  Use.     69 


A  Dairy  Laboratory  Guide 


THE   COMPOSITION ' 


Milk  is  composed  of  a  great  many  substances, 
but,  so  far  as  the  dairyman  is  concerned,  there  are 
only  six  constituents  which  are  of  prime  impor- 
tance. The  following  table  gives  the  constituents 
of  milk,  together  with  the  per  cent  of  each,  ob- 
tained by  a  large  number  of  analyses : 

Water 87 .  o  per  cent 

Fat    4.0  per  cent 

Casein    2.6  per  cent 

Sugar    5.0  per  cent 

Albumen 0.7  per  cent 

Ash    0.7  per  cent 

Although  in  the  above  table  the  different  con- 
stituents are  given  definite  per  cents,  yet  the  com- 
position of  normal  milk  is  very  variable.  The 
water  needs  no  discussion,  as  it  is  just  like  the  water 
found  anywhere  else  in  nature. 

Fat  is  present  in  milk  in  the  form  of  minute  drop- 
lets or  globules.  These  globules  are  distributed 
throughout  the  milk  and  are  not  in  solution,  but 
in  fine  suspension.  This  state  is  called  an  emulsion. 
It  was  disputed  for  a  long  time  as  to  whether  or  not 
the  fat  globule  had  a  membrane  around  it.  It  is 
now  believed  by  the  best  authorities  that  the  fat 
globule  has  no  membrane,  but  that  the  droplet 


2  A  DAIRY   LABORATORY   GUIDE 

keeps  its  circular  form  because  of  its  power  of  con- 
densing upon  its  surface  the  serum  of  the  milk. 
The  size  of  the  fat  globules  differ  in  milk  from 
Different  breeds  qf  cows,  and  it  is  supposed  that  the 
larger  ^tfre  'faM>  globules  the  more  easily  they  rise  to 
when  'the  milk  is  left  standing  in  a 


Butter  is  composed  largely  of  fat,  so  we  speak  of 
the  fat  of  milk  as  butter  fat. 

Fat  is  the  most  important  constituent  of  the 
milk,  because  milk  which  contains  a  fair  amount  of 
butter  fat  is  more  valuable  as  a  food  than  a  milk 
which  is  poor  in  fat.  The  other  food  constituents 
of  the  milk  usually  increase  or  decrease  as  the  fat 
increases  or  decreases.  This  is  true,  however,  only 
within  certain  limits. 

Fat  is  an  important  constituent  of  nearly  all  of 
the  products  of  milk,  so  that  in  most  cases  a  milk 
rich  in  fat  is  more  valuable  for  manufacturing  pur- 
poses than  a  milk  poor  in  fat. 

On  account  of  the  importance  of  the  fat,  it  is 
made  oftentimes  a  basis  of  payment  for  milk. 

Butter  fat  is  composed  mainly  of  nine  different 
fats.  There  are  a  few  fats  which  are  present  in 
such  minute  quantities  that  they  are  of  no  prac- 
tical importance.  All  of  the  fats  have  the  same 
basis,  namely,  glycerin,  and  the  fat  is  made  by  the 
chemical  union  of  glycerin  and  the  corresponding 
fatty  acid.  For  example,  the  fat  butyrin  is  made 
of  glycerin  and  butyric  acid.  The  fat  stearin  is 
made  of  stearic  acid  and  glycerin.  While  the  com- 
position of  the  different  butter  fats  are  known,  yet 
the  chemist  is  unable  to  make  them  in  the  labora- 
tory. 

The  fats  of  butter  fat  are  divided  into  two  main 
groups,  the  volatile  and  nonvolatile,  and  are  so 


A   DAIRY   LABORATORY   GUIDE  3 

named   because   they   are   made    respectively   from 
volatile  and  nonvolatile  fatty  acids. 

The  fats  under  each  class  are  as  follows: 

VOLATILE  NONVOLATILE 

Butyrin  Olein 

Caprin  Myristin 

Caproin  Palmatin 

Caprillin  Stearin 
Laurin 

There  is  some  dispute  as  to  whether  laurin  is  a 
volatile  or  nonvolatile  fat,  but  it  is  usually  consid- 
ered volatile.  The  volatile  fats  compose  about  8 
per  cent  and  the  nonvolatile  about  92  per  cent  of 
butter  fat.  The  fats  of  butter  fat  have  different 
characteristics  and  properties,  and  one  chief  dif- 
ference of  fats  is  their  melting  point.  For  example 
the  melting  point  of  stearin  is  about  143°  F.,  and 
the  melting  point  of  olein  is  about  40°  F.  A  varia- 
tion in  the  amount  of  either  of  these  two  fats  would 
necessarily  cause  the  melting  point  of  butter  fat  to 
vary.  The  melting  point  of  butter  fat  is  usually 
between  92°  F.  and  96°  F. 

Casein  is  the  chief  proteid  compound  of  milk,  and 
forms  about  20  per  cent  to  23  per  cent  of  the  milk 
solids.  It  exists  in  milk  in  very  fine  suspension, 
and  is  held  in  suspension  by  the  salts  of  calcium. 
It  is,  therefore,  sometimes  called  calcium  casein. 
The  casein  is  in  such  a  fine  state  of  suspension  that 
it  cannot  be  filtered  out  of  the  milk  by  any  ordinary 
means.  This  fine  state  of  suspension  is  called  the 
collodial  state.  When  milk  sours  naturally  and 
enough  acid  is  found  to  unite  with  the  lime  salts 
of  the  milk,  the  casein  is  precipitated.  Casein  is 
also  precipitated  by  any  acid  and  rennet  or  pepsin. 
Casein  is  valuable  as  food  both  in  raw  milk  and  in 


4  A   DAIRY   LABORATORY   GUIDE 

the  products  of  milk,  such  as  the  various  kinds  of 
cheese.  It  is  also  used  commercially  in  many 
ways,  some  of  them  being  as  a  substitute  for  cel- 
luloid in  the  manufacture  of  buttons  and  toilet 
articles.  It  is  also  used  in  cold  water  paints.  By 
a  new  process  it  is  said  that  casein  is  now  being 
made  into  a  substitute  for  ivory,  making  excellent 
table  tops,  mantels,  etc. 

Sugar  forms  about  37  per  cent  to  39  per  cent  of 
the  milk  solids.  The  chief  value  of  milk  sugar  is 
its  food  value  in  milk.  It  is  also  used  in  pharmacy 
in  mixing  powders,  coating  pills,  etc.  Milk  sugar 
is  not  used  very  extensively  commercially  because 
of  the  expensive  cost  of  manufacture.  It  is  not 
as  sweet  as  cane  sugar,  because  it  is  not  as  soluble. 
It  has  the  same  chemical  formula  (CioH^On) 
as  cane  sugar.  Acid  is  produced  naturally  in  milk 
by  the  action  of  bacteria  upon  the  milk  sugar. 

The  albumen  in  milk  is  in  solution.  It  is  valu- 
able chiefly  as  a  food  in  milk.  It  has  one  commer- 
cial use  in  the  manufacture  of  Italian  cheese.  This 
cheese  is  made  where  large  quantities  of  whey  are 
produced.  The  whey  is  heated  nearly  to  the  boil- 
ing point,  and  this  heat  precipitates  the  albumen. 
The  whey  is  then  drawn  off  and  the  albumen  is 
dipped  into  molds.  The  cheese  made  from  albumen 
forms  a  very  good,  nutritious  food. 

The  ash  is  the  part  of  milk  left  after  burning,  and 
it  is  the  most  constant  constituent  of  the  milk. 
It  very  rarely  goes  below  .68  per  cent  or  above  .72 
per  cent.  It  consists  chiefly  of  the  phosphates  of 
calcium  and  the  chlorides  of  sodium,  potassium, 
iron  and  magnesia. 

Ash  is  important  as  a  food  in  furnishing  the 
mineral  constituents  for  the  body. 


A   DAIRY    LABORATORY    GUIDE  5 

THE    BABCOCK   TEST 

The  Babcock  test  is  a  test  for  the  per  cent  of  fat 
in  milk  and  its  products.  It  was  invented  by  Dr. 
S.  M.  Babcock,  chief  chemist  for  the  experiment  sta- 
tion at  Wisconsin,  and  a  description  of  the  test  was 
published  in  a  report  of  1890  from  that  station. 
The  instrument  used  to  measure  the  milk  is  called 
a  pipette  and  holds  up  to  its  graduated  mark  17.6 
cc.  Since  milk  is  somewhat  viscous,  the  pipette 
will  deliver  on  an  average  17.44  cc.,  which  is  for 
all  practical  purposes  18  grams.  In  using  the 
pipette  the  milk  is  drawn  above  the  17.6  cc.  mark 
and  the  soft  part  of  the  index  finger  placed  quickly 
over  the  pipette.  The  column  of  milk  can  be 
easily  controlled  and  allowed  to  flow  out  until  it  is 
on  a  level  with  the  17.6  cc.  mark.  The  pipette 
should  always  be  held  so  that  the  17.6  cc.  mark  is 
on  a  level  with  the  eye.  The  sample  to  be  tested 
is  measured  into  a  special  bottle  with  a  graduated 
neck,  holding  a  column  of  melted  fat  which  is  a 
definite  per  cent  by  weight  of  the  18  grams  of  milk 
taken.  In  adding  the  milk  to  the  bottle  the  latter 
should  be  held  in  a  slanting  position,  so  that  the 
milk  will  run  down  the  lower  inside  of  the  bottle 
neck  and  will  not  be  forced  out  by  the  outcoming 
air. 

After  measuring  the  milk  into  the  bottle,  17.5 
cc.  of  sulphuric  acid  (H^SC^)  of  a  specific  gravity 
of  1.82  to  1.83  is  added  and  the  milk  and  acid  at 
once  thoroughly  mixed.  The  acid  burns  up  (by 
moist  combustion)  everything  in  the  milk  except- 
ing the  fat.  The  same  precautions  should  be  ob- 
served in  adding  the  acid  as  in  adding  the  milk, 
namely,  to  slant  the  bottle,  and  the  bottle  should  be 
revolved  as  the  acid  is  poured  in,  so  that  all  of 


6  A   DAIRY    LABORATORY    GUIDE 

the  milk  adhering  to  the  neck  of  the  bottle 
will  be  washed  down.  The  vessel  contain- 
ing the  acid  should  be  kept  corked  in  order 
to  prevent  the  acid  taking  up  moisture  from  the  air 
and  becoming  too  weak  for  use.  If  the  acid  is  too 
weak  more  than  17.5  cc.  are  used,  and  if  too  strong 
less  than  17.5  cc.  are  used.  Good  acid  is  colorless, 
although  it  may  be  quite  dark  and  at  the  same  time 
be  useful  for  the  Babcock  test.  It  must,  in  any 
case,  be  free  from  undissolved  foreign  particles. 

After  adding  the  acid  to  the  milk  the  bottles  are 
placed  in  a  centrifugal  machine  and  whirled.  Care 
should  be  taken  to  have  the  machine  balanced,  i.  e., 
for  every  bottle  on  one  side  of  the  machine  there 
should  be  a  corresponding  bottle  on  the  opposite 
side  of  the  machine.  The  bottles  are  centrifuged 
for  five  minutes  and  then  filled  with  hot  water  up 
to  the  base  of  the  neck.  Centrifuging  is  then  con- 
tinued for  two  minutes  more  and  hot  water  is  added 
to  bring  the  fat  into  the  graduated  neck.  The  cen- 
trifuge is  then  run  for  one  minute. 

The  bottles  are  then  ready  to  read,  and  in  case 
of  whole  milk  one  should  read  between  the  extreme 
points  of  the  fat  column.  This  method  of  reading, 
by  comparison  with  the  chemical  method,  has  been 
found  to  make  up  for  the  fat  which  remains  in 
the  bottom  of  the  bottle  and  cannot  be  removed  by 
centrifuging.  The  bottles  should  be  read  at  a  tem- 
perature of  120°  F.  It  is  no  trouble  to  obtain  this 
temperature  if  centrifuging  has  been  done  with  a 
steam  machine.  Where  the  machine  is  filled  with 
steam  the  bottles  should  stand  for  from  thirty 
seconds  to  one  minute  in  a  room  at  ordinary  tem- 
perature to  allow  excess  of  heat  to  pass  off  before 
reading.  If  a  hand  machine  is  used  the  tester  must 
have  hot  water  placed  in  it  to  obtain  the  required 


A   DAIRY    LABORATORY    GUIDE  7 

temperature.  This  is  especially  necessary  if  the 
testing  is  being  done  in  a  cold  room. 

The  machine  should  always  be  kept  well  oiled 
and  securely  fastened  to  the  support  on  which  it  is 
being  operated.  Skimmed  milk  contains  such  a 
small  amount  of  fat  that  the  fat  column  could  not  be 
read  in  an  ordinary  whole  milk  bottle.  A  bottle  is, 
therefore,  used  which  has  a  neck  with  a  small  bore. 
This  neck  is  so  small  that  the  milk  and  acid  could 
not  be  poured  through  it,  so  a  funnel  tube  is  pro- 
vided for  this  purpose.  The  skimmed  milk  bottle 
should  be  placed  in  the  machine  in  such  a  position 
that  the  funnel  tube  will  be  on  the  outside.  This 
will  prevent  fat  lodging  in  the  space  between  the 
tube  and  the  wall  of  the  bottle. 

The  sulphuric  acid  is  added  to  the  milk  to 
destroy  all  of  the  milk  solids  except  the  fat,  and  the 
chief  solid  to  be  destroyed  is  the  casein.  Skimmed 
milk  contains  proportionately  more  casein  than 
does  whole  milk  and,  therefore,  in  making  a  Bab- 
cock  test  of  skimmed  milk  2  cc.  extra  of  sulphuric 
acid  should  be  used.  The  fat  globules  in  skimmed 
milk  are  small  in  size  and  correspondingly  hard  to 
remove.  A  Babcock  sample  of  skimmed  milk 
should,  therefore,  be  whirled  ten  minutes,  two 
minutes  and  one  minute. 

Cream  is  so  viscous  that  it  cannot  be  measured 
accurately  into  a  test  bottle  by  means  of  a  pipette 
It  should  always  be  weighed.  The  New  York  state 
dairy  laws  now  consider  it  a  misdemeanor  to  meas- 
ure cream  for  testing  where  the  tests  are  used  as  a 
basis  of  payment  for  butter  fat. 

Because  the  cream  is  sometimes  too  rich  in  butter 
fat  to  be  tested  in  an  ordinary  cream  bottle,  9 
grams  are  tested  in  place  of  18  grams  and  the  result 
multiplied  by  two.  Nine-gram  cream  bottles  are 


8  A   DAIRY    LABORATORY    GUIDE 

also  coming  into  common  use.  These  bottles  give 
the  reading  direct  without  any  computation.  In 
testing  9  grams  one  would  naturally  use  one-half 
"the  usual  amount  of  sulphuric  acid.  On  account, 
however,  of  the  large  proportion  of  fat  present,  the 
acid  is  liable  to  char  the  fat ;  and  for  this  reason  it 
is  better  to  add  approximately  9  grams  of  water 
and  then  add  a  little  less  than  the  usual  amount  of 
acid. 

Butter  is  tested  in  the  cream  bottles,  from  3  to  4 
grams  being  used  for  the  test.  Enough  warm 
water  is  added  to  bring  the  sample  up  to  approx- 
imately 18  grams,  and  from  10  to  12  cc.  of  the  sul- 
phuric acid  are  used. 

Cheese  is  also  tested  in  the  cream  bottle,  4  to  5 
grams  being  used.  The  cheese  must  first  be  minced 
with  a  knife  as  fine  as  possible  in  order  to  make  it 
possible  for  the  acid  to  dissolve  all  of  the  casein. 
After  the  cheese  is  weighed  into  the  bottle,  about 
5  cc.  of  hot  water  are  added  and  the  mixture  shaken 
vigorously  for  two  or  three  minutes.  This  softens 
the  casein.  Enough  hot  water  is  then  added  to 
bring  the  sample  to  approximately  18  grams.  The 
sample  is  again  shaken  for  two  or  three  minutes, 
and  the  ordinary  amount  of  H2SO4  is  then  added. 
If  the  cheese  is  old  and  dry,  2  or  3  cc.  of  H2SO4  in 
excess  of  the  usual  amount  are  sometimes  necessary 
to  dissolve  the  casein.  In  mincing  the  cheese  the 
sample  should  not  be  allowed  to  dry  out  any  more 
than  is  absolutely  necessary. 

In  the  cases  of  both  the  butter  and  the  cheese, 
the  results  obtained  must  be  reduced  to  an  1 8-gram 
basis,  because  the  bottles  are  graduated  for  that 
amount.  This  can  be  done  by  dividing  the  per  cent 
obtained  by  the  number  of  grams  used  and  multiply 
the  quotient  by  18. 


A   DAIRY    LABORATORY    GUIDE  Q 

Whey  is  usually  tested  in  whole  milk  bottles, 
although  it  is  best  to  test  it  in  skimmed  milk  bot- 
tles when  possible.  The  right  bottle  to  use  can 
only  be  determined  by  actual  experiment.  Whey 
requires  less  acid  than  whole  milk,  usually  about 
12  cc. 


EXERCISES 


12  A  DAIRY  LABORATORY  GUIDE 

EXERCISE  I 
THE  BABCOCK  TEST 

1.  Draw  the  milk  above  the  mark  on  the  pipette 

and  allow  the  milk  to  settle  just  to  the  mark. 
Repeat  this  until  some  proficiency  in  the  use  of 

the  pipette  is  obtained. 
What  two  special  precautions  are  to  be  observed 

in  handling  the  pipette? 

2.  Test  by  the  Babcock  method  a  sample  of  whole 

milk.  Perform  this  test  before  doing  either 
3  or  4. 

3.  Measure  out  into  your  white  cup  50  cc.  of  the 

same  sample  of  milk  used  in  experiment  2. 
Add  to  this  15  cc.  of  water.  Mix  thoroughly 
and  test  in  duplicate  by  the  Babcock  method. 

4.  Using  milk  from  the   same  sample  as  used  in 

experiment  2,  measure  out  qo  cc.  of  milk  and 
add  to  it  15  cc.  of  skimmed  milk.  Mix  thor- 
oughly and  test  in  duplicate  by  the  Babcock 
method. 

Did  you  obtain  the  most  fat  in  experiment  3  or 
experiment  4?  Include  in  your  notes  a  brief 
description  of  the  Babcock  test. 


A  DAIRY  LABORATORY  GUIDE  13 

STUDENT'S  NOTES  AND  REPORT 


14  A  DAIRY   LABORATORY   GUIDE 

STUDENT'S    NOTES   AND    REPORT 


A  DAIRY  LABORATORY  GUIDE  1 5 

EXERCISE  II 
BABCOCK  TEST 

1.  Test  in  duplicate  a  sample  of  whole  milk,  skimmed 

milk  and  cream.     Test  the  skimmed  milk  in 

the  same  way  that  the  whole  milk  is  tested. 
Why  is  cream  taken  by  weight  instead  of  by 

volume? 

Why  are  9  grams  used  instead  of  18  grams? 
When  9  grams  of  cream  are  tested  in  an  18- 

gram  bottle,  what  correction  has  to  be  made 

in  the  result  and  why? 

2.  Retest  the  cream  and  skimmed  milk.     Add  acid 

to  the  skimmed  milk  about  one-fourth  of  an 
inch  above  the  mark  and  whirl  ten  minutes 
the  first  time,  two  minutes  the  second  time 
and  one  minute  the  third  time. 

In  retesting  the  cream  do  not  add  water,  and 
use  one-half  the  usual  amount  of  acid. 

In  order  to  save  time  the  cream  and  skimmed 
milk  may  be  whirled  together. 

Explain  fully  the  object  of  using  extra  acid  and 
whirling  an  extra  length  of  time  in  testing 
skimmed  milk. 

Record  carefully  any  difference  in  the  appear- 
ance of  the  fat  column  of  the  cream  in  ex- 
periments i  and  2. 

What  should  be  the  appearance  of  an  ideal  fat 
column  in  a  completed  Babcock  test? 


1 6  A  DAIRY   LABORATORY   GUIDE 

STUDENT'S    NOTES    AND    REPORT 


A  DAIRY  LABORATORY  GUIDE  I? 

STUDENT'S  NOTES  AND  REPORT 


l8  A  DAIRY   LABORATORY   GUIDE 

EXPLANATION    OF    BOILED    MILK    TEST 
AND    FORMALDEHYDE    TEST 

There  are  two  principal  tests  for  boiled  milk. 
One  test  makes  use  of  three  chemicals — hydrogen 
peroxide,  potassium  iodide  and  starch.  In  the 
second  test  two  reagents  are  employed — hydrogen 
peroxide  and  paraphenylenediaminehydrochloride. 
In  both  cases  a  blue  color  results  if  the  milk  has 
not  been  boiled.  If  the  milk  has  been  boiled  no 
blue  color  will  result.  The  last  named  test  acts 
more  rapidly  than  the  first  one  and  also  gives  a 
more  intense  color.  Any  double  oxide  may  be  sub- 
stituted in  place  of  the  hydrogen  peroxide.  Such  a 
double  oxide  would  be  calcium  peroxide.  There  is 
in  milk  an  enzyme  galactase  which  is  destroyed  by 
heat.  When  the  milk  has  not  been  heated  this 
enzyme  sets  free  the  oxygen  from  the  oxidizing 
agent,  and  in  case  of  the  first  test,  the  free  oxygen 
splits  up  the  potassium  iodide  and  liberates  free 
iodine.  The  starch  in  the  presence  of  free  iodine 
turns  blue.  In  case  of  the  second  test  the  oxygen 
liberated  by  the  galactase  acts  directly  on  the 
paraphenylenediaminehydrochloride  and  turns  the 
solution  blue.  Hydrogen  peroxide  often  contains 
sulphuric  acid.  When  this  is  the  case,  the  reagent 
is  useless  for  the  test  with  starch,  as  the  free  acid 
would  break  up  the  potassium  iodide.  If  this  hap- 
pened a  blue  color  would  result  whether  the  milk 
had  been  heated  or  not. 

The  test  for  formaldehyde  is  a  delicate  one  and 
is  easy  to  perform,  inasmuch  as  it  may  be  done  in 
connection  with  the  Babcock  test.  The  regular 
amount  of  milk  is  measured  with  the  17.6  cc.  pipette 
into  a  Babcock  test  bottle  and  a  few  drops  of  ferric 
chloride  added.  The  regular  amount  of  sulphuric 


A   DAIRY    LABORATORY   GUIDE  1 9 

acid  is  next  added,  and  if  formaldehyde  is  present 
a  lavender-colored  ring  will  appear  between  the 
layer  of  acid  and  the  layer  of  milk.  If  the  contents 
of  the  bottle  are  slowly  mixed  the  dissolving  casein 
will  take  on  a  lavender  color.  The  test  will  not 
work  if  the  milk  is  too  old  or  if  too  much  of  the 
formaldehyde  has  been  added  to  the  milk. 

Sometimes  sulphuric  acid  contains  ferric  salts  as 
an  impurity;  and  when  such  is  the  case,  the  acid 
will  give  the  test  for  formaldehyde  without  the  use 
of  ferric  chloride.  It  is  best  however,  to  always 
add  the  ferric  chloride  to  make  sure  there  is  a  ferric 
salt  present. 

EXPLANATION.       MIXING      SAMPLES      OF 

BUTTER  BEFORE  TESTING  FOR  FAT 

OR    MOISTURE 

Before  testing  a  sample  of  butter  for  either 
moisture  or  fat  the  sample  should  be  thoroughly 
mixed.  Fat  and  water  do  not  readily  mix,  and 
special  precautions  must  be  taken  to  make  the 
sample  uniform  throughout.  The  butter  should  be 
heated  and  stirred  until  it  is  about  the  consistency 
of  thick  cream.  Do  not  heat  the  butter  too  much, 
as  the  water  and  fat  will  entirely  separate  and  it  is 
difficult  to  remix  them  again.  The  sample  should 
then  be  cooled  and  stirred  thoroughly  while 
cooling,  else  the  fat  will  cool  rapidly  on  the 
outside  and  force  all  of  the  water  towards 
the  middle  of  the  sample.  The  cooling  process 
should  be  kept  up  until  the  sample  is  quite  firm. 
The  heating  and  cooling  may  be  accomplished  by 
placing  the  butter  in  any  convenient  vessel,  such 
as  a  glass-stoppered  sample  jar.  The  jar  may  then 
be  held  under  a  water  faucet  or  set  in  a  dish  of 
water. 


2O  A   DAIRY    LABORATORY    GUIDE 

EXERCISE  III 
BABCOCK    TEST 

1.  Test  by  the  Babcock  method  a  sample  of  whole 

milk,  skimmed  milk  and  butter. 
Mix  the  butter  properly  before  weighing  it  out 
for  the  test. 

2.  Measure  out  about  36  grams  of  skimmed  milk 

(Babcock  pipette  twice  full  to  the  mark). 
Divide  approximately  into  four  parts.  Test 
two  of  these  parts  for  boiling  by  two  dif- 
ferent methods.  Boil  the  remaining  18 
grams,  divide  approximately  into  two  parts 
and  test  for  boiling  by  two  different  methods. 
Give  the  chemicals  used  in  each  case.  Do 
not  add  the  chemicals  to  the  milk  while  the 
milk  is  hot. 

3.  Measure  out  in  duplicate  a  sample  of  skimmea 

milk  as  for  the  Babcock  test.  Before  adding 
the  sulphuric  acid  dip  your  stirring  rod  into 
the  formaldehyde  and  rinse  it  off  in  one  of 
the  samples.  Then  add  to  both  samples  the 
ferric  chloride  and  sulphuric  acid  and  note 
the  difference  in  color  due  to  formaldehyde. 

4.  Test   any   four   of   the    samples    furnished,    for 

formaldehyde.     Report  by  number. 
Sometimes   sulphuric   acid   will   alone   give   the 

color  test  for  formaldehyde.     Why  is  this? 
Why  is  it  best  to  always  add  the  ferric  chloride 

when  making  the  formaldehyde  test? 


A  DAIRY  LABORATORY  GUIDE  21 

STUDENT'S  NOTES  AND  REPORT 


22  A  DAIRY   LABORATORY   GUIDE 

STUDENT'S   NOTES   AND    REPORT 


A   DAIRY    LABORATORY    GUIDE  23 

THE  C.  U.  BUTTER  MOISTURE  TEST 

When  butter  is  heated  over  a  flame,  the  casein 
forms  a  snow-white  blanket  over  the  surface  of  the 
butter.  By  a  comparison  with  the  chemical  method 
it  has  been  found  that  when  the  butter  loses  its 
snow-white  color  and  turns  a  dirty  brown  color  the 
sample  has  given  up  its  moisture.  When  this 
brown  color  has  appeared  it  is  time  to  remove  the 
sample  from  the  flame.  Heating  butter  in  a  direct 
flame  is  liable  to  volatilize  some  of  the  butter,  even 
before  all  of  the  water  has  been  given  off.  In  order 
to  do  away  with  this  danger  a  sheet  of  asbestos  is 
placed  between  the  flame  and  the  container  of  the 
sample.  The  asbestos  so  tempers  the  flame  that 
while  a  high  heat  is  produced,  the  danger  of  sud- 
denly volatilizing  the  butter  is  largely  done  away 
with. 

The  scales  used  are  made  especially  for  use  in 
butter-moisture  work.  They  are  so  constructed 
that  after  the  moisture  is  driven  off,  each  notch 
the  large  weight  is  reversed  equals  I  per  cent  of 
moisture  driven  off,  and  each  notch  that  the  small 
weight  is  reversed  equals  .1  per  cent  of  moisture 
driven  off.  Always  allow  the  sample  to  cool  be- 
fore weighing.  While  the  sample  is  cooling  it  is 
well  to  cover  it  with  something  fa  sheet  of  paper 
will  do),  so  that  the  sample  will  not  take  water 
from  the  air. 


24  A   DAIRY    LABORATORY    GUIDE 


EXERCISE  IV 

BABCOCK  TEST  AND  BUTTER  MOISTURE 
TEST 

1.  Prepare  a  sample  of  butter  for  the  moisture  test 

and  test  by  the  C.  U.  method. 

2.  Test  a  sample  of  milk  in  the  ordinary  way. 
Retest  the  same  sample  in  duplicate,  using  only 

9  grams  of  the  sample.  (It  must  be  weighed 
out.)  Make  the  sample  up  to  18  grams  by 
adding  water.  Add  the  usual  amount  of 
acid. 

3.  Test  a  sample  of  cream  in  the  ordinary  way. 
Retest  the  cream  in  the  whole  milk  bottle,  divid- 
ing   18    grams    between    four    bottles    (4^2 
grams  by  weight  in  each  bottle). 

In  each  case  add  enough  water  to  bring  the 
sample  up  to  18  grams  and  then  add  the 
proper  amount  of  acid  as  indicated  by  the 
appearance  of  the  sample.  Add  the  acid 
slowly,  a  little  at  a  time,  and  shake  thor- 
oughly. 


A  DAIRY  LABORATORY  GUIDE  25 

STUDENT'S  NOTES  AND  REPORT 


26  A  DAIRY   LABORATORY   GUIDE 

STUDENT'S    NOTES   AND    REPORT 


A   DAIRY    LABORATORY    GUIDE  2? 

THE    SPECIFIC    GRAVITY    OF    MILK    AND 
THE    LACTOMETER 

The  specific  gravity  or  density  of  a  substance  is 
a  ratio  between  the  weight  of  a  given  volume  of 
the  substance  and  the  weight  of  a  given  volume  of 
some  other  substance  taken  as  a  standard.  The 
standard  for  liquids  is  water  and  its  specific  gravity 
is  taken  as  one.  Milk  is  slightly  heavier  than  water, 
and  the  specific  gravity  of  normal  milk  averages 
1.032,  and  the  specific  varies  from  1.029  to  1.035. 
If  we  add  water  to  milk  the  specific  gravity  is 
lowered,  because  water  is  lighter  than  milk;  and  if 
we  skim  milk  we  take  away  fat  which  is  lighter 
than  milk  and  the  specific  gravity  is  increased. 
When  the  water  is  added  to  milk  the  effect  is  the 
same  as  it  would  be  if  the  solids  were  actually  re- 
moved from  the  milk.  This  is  true  because  the 
solids  which  were  distributed  throughout  a  given 
volume  on  the  addition  of  water,  have  to 
distribute  themselves  throughout  the  increased 
volume  of  the  liquid.  For  this  reason  we  say 
that  the  addition  of  water  to  milk  "  decreases " 
the  total  solids,  and  it  is  a  fact  that  when  water  is 
added  to  milk  all  of  the  solids  are  decreased  in  the 
same  proportion.  It  is  important  to  remember 
this  fact  when  one  is  figuring  out  the  per  cent  of 
adulteration  of  milk. 

THE  LACTOMETER. — The  instrument  used  to 
measure  the  specific  gravity  of  a  liquid  is  called  a 
hydrometer,  and  there  are  many  kinds  of  specialized 
hydrometers.  The  hydrometer  used  to  test  the 
density  of  milk  is  called  a  lactometer,  and,  for  the 
most  part,  only  two  kinds  are  used.  One  of  these 
is  called  the  Quevenne  (called  Q.  for  abbreviation) 
and  the  other  is  called  the  New  York  State  Board  of 


28  A  DAIRY   LABORATORY   GUIDE 

Health  (commonly  called  the  B.  of  H.  lactometer). 

The  Quevenne  lactometer  has  a  long,  narrow 
stem  which  is  extended  into  a  hollow  glass  tube  of 
much  larger  diameter  than  the  stem  itself.  At  the 
lower  end  of  the  instrument  is  a  bulb  of  mercury 
which  causes  the  lactometer  to  sink  in  the  liquid 
to  its  proper  level.  The  upper  part  of  the  stem 
contains  a  thermometer  scale,  as  it  is  important  to 
know  the  temperature  of  the  milk  when  the  lac- 
tometer reading  is  taken.  This  scale  does  not  re- 
cord high  temperature,  and,  therefore,  the  instru- 
ment should  never  be  placed  in  hot  liquids.  In 
order  to  clean  the  lactometer  wash  in  cool  water 
and  wipe  with  a  dry  cloth.  Immediately  below  the 
thermometer  scale  is  a  lactometer  scale  with  num- 
bers ranging  from  15  to  45,  the  lowest  readings 
being  at  the  upper  end  of  the  scale.  One  may  ob- 
tain the  specific  gravity  reading  by  prefixing  i.o 
before  the  lactometer  reading.  Thus,  if  the  in- 
strument gives  a  reading  of  33,  the  specific  gravity 
would  be  1.033.  The  fact  that  the  Quevenne  lac- 
tometer gives  specific  gravity  readings  directly  is 
one  of  its  chief  advantages. 

Temperature  affects  the  density  of  liquids.  The 
colder  the  milk  the  more  dense  it  is,  and  the  warmer 
the  milk  the  less  dense  it  is.  For  this  reason  lac- 
tometers are  standardized  to  give  readings  at  a 
temperature  of  60°  F.  When  milk  is  warmer  or 
colder  than  60°  F.  a  correction  must  be  made,  and 
this  correction  for  the  Quevenne  is  .1  of  a  lactometer 
degree  for  every  degree  in  temperature  that  the 
sample  is  above  or  below  the  standard  temperature. 
When  we  cool  the  milk  down  we  add ;  when  we 
warm  the  milk  we  subtract.  For  example,  if  a 
lactometer  gave  a  reading  of  32  at  a  temperature 
of  66°  R,  we  would  add  .6  (.1X6)  to  the  lactometer 


A  DAIRY    LABORATORY   GUIDE  2Q 

reading,  making  the  corrected  or  true  reading  32.6. 
In  this  case  the  specific  gravity  would  be  1.0326. 

Familiarity  with  the  action  of  the  lactometer  may 
be  obtained  by  working  theoretical  problems,  of 
which  the  following  is  an  illustration :  If  the 
lactometer  reading  of  a  sample  of  milk  is  31.5  at 
62°  F.,  what  would  be  the  reading  at  57°  F.?  In 
this  case  57°  F.  becomes  our  standard,  because  it  is 
the  temperature  to  which  we  are  going  to  lower  the 
sample.  Since  the  sample  is  5  degrees  too  warm, 
•5  (^XS)  of  a  lactometer  degree  must  be  added  to 
the  lactometer  reading,  making  the  true  or  cor- 
rected lactometer  reading  32. 

When  used  in  connection  with  theBabcock  test  the 
lactometer  reading  is  important  in  obtaining  the  total 
solids  and  solids  not  fat  of  milk.  There  are  several 
of  these  formulae  in  use,  and  while  they  do  not  give 
quite  as  accurate  results  as  the  chemical  method, 
they  give  results  which  are  accurate  enough  for  all 
practical  purposes.  They  are  as  follows : 
*  i.  ^=S.  N.  F.  Babcock's  formulae. 

2.  1^=5.  N.  F.  Troy's  formulae. 

3.  Y4    L+.2f+.i4=S.   N.   F.   Babcock's  modi- 

fied formula. 

Generally  speaking,  the  first  formula  gives  the 
highest  results,  the  second  next  highest  and  the 
third  the  lowest  results.  One  can  find  the  total 
solids  by  adding  the  fat  reading  to  the  solids  not 
fat.  In  these  formulae  L  stands  for  the  lactometer 
reading  and  F  for  the  fat  reading. 

In  using  these  formulae,  the  following  precautions 
must  be  especially  noted :  Board  of  health  readings 
can  never  be  used  in  these  formulae,  consequently 
B.  of  H.  readings  must  be  changed  to  Q. ;  specific 
gravity  readings  cannot  be  used;  the  per  cent  of 
fat  expressed  in  hundredths  cannot  be  used. 


3<D  A  DAIRY   LABORATORY   GUIDE 

An  illustrative  example  will  show  how  these 
formulae  operate.  Suppose  the  Q.  lactometer  read- 
ing1 of  a  sample  of  milk  was  32.5  at  60°  F.  and  the 
fat  reading  was  4.2  per  cent,  what  are  the  solids 
not  fat? 
Formula= 

I.     ^±f=S.  N.  F.  .7X4-2—2.94 
2.94+32.5=35.44 
35.44-^-3.8=9.32+ 
Formulating  the  above  calculation : 
•32-5+2-94  =9.32%  S.  N.  F. 
9.32+4.2=13.52  total  solids. 
Using  formula  2 : 
i^=S.  N.  F. 
32.5+4.2=36.7 
36.7-^-4=9.17+%  S.  N.  F. 
Formulating  the  above  calculation : 
2*$±"=9.i7  S.  N.  F. 
9.17+4.2=13.37  T.  S. 
Using  formula  3 : 

#L+.2f+.i4=S.  N.  F. 
32.5-^-4=8.12 

.2X4.2^.84 

8.i2+.84+.i4=9-io  S.  N.  F. 

9.10+4.2=13-30  T.  S. 

By  modifying  Babcock's  third  formula  the  total 
solids  may  be  obtained  directly.  It  is  as  follows: 

y4  L+i.2f+.i4=T.  S. 

Using  the  above  lactometer  and  fat  readings  as 
an  illustration,  the  formula  would  give  the  following 
results : 

32.5-^4=8.12 

1.2X4.2=5.04 
8.i2+5.04+.i4=i3-30%  S.  N.  F. 


A  DAIRY   LABORATORY   GUIDE  3! 

The  following  example  will  illustrate  how  a 
knowledge  of  the  per  cent  of  S.  N.  F.  of  a  sample 
of  milk  is  utilized  in  figuring  adulteration  per  cents : 

Before  adulteration  a  sample  of  milk  had  4.2  per 
cent  of  fat  and  9.0  per  cent  of  S.  N.  F.  After  adul- 
teration the  sample  contained  3.1  per  cent  fat  and 
7.5  per  cent  of  S.  N.  F.  The  following  questions 
can  be  answered  from  calculations  with  the  above 
data: 

1.  What  per  cent  of  water  was  added  to  the 

milk? 

2.  At  what  rate  per  cent  was  the  water  added? 

3.  What  per  cent  of  the  fat  was  adulterated 

by  skimming? 

4.  What  per  cent  of  the  fat  was  adulterated 

by  watering? 

(1)  Since  there  were  9  parts  of  S.  N.  F.  before 
adulteration  and  7.5  parts  of  S.  N.  F.  after  adultera- 
tion, 1.5  must  have  been  removed  by  adulteration. 

9—7-5=1.5 

1.5-^-9=16.66%  of  S.  N.  F.  removed  by  adding 

the  water. 

Since  16.66  per  cent  of  S.  N.  F.  was  removed, 
water  is  the  only  thing  that  could  have  taken  its 
place;  therefore  16.66  per  cent  of  water  was  added 
to  the  milk. 

(2)  For  every  7.5  parts  of  S.  N.  F.  in  the  milk 
1.5   parts  were  removed,  or  in  other  words  water 
was  added  at  the  rate  of  1.5  parts  of  water  to  every 
7.5  of  S.  N.  F. 

The  rate  per  cent  at  which  water  was  added 
would  be  i. $-7-7.5=20%. 

Before  adulteration  the  sample  had  4.2  parts  fat 
and  after  adulteration  3.1  parts  fat,  i.i  parts  of  fat 
were  removed,  which  equals  26.19  per  cent. 
1.1-7-4.2=26.19%. 


32  A  DAIRY   LABORATORY   GUIDE 

When  milk  is  watered  all  of  the  solids  are  re- 
duced in  the  same  proportion.  It  has  been  found  that 
16.66  per  cent  of  the  S.  N.  F.  was  removed  by  water- 
ing; therefore,  according  to  the  above  rule  16.66  per 
cent  of  the  fat  must  have  been  removed  by  water- 
ing. But  26.19  per  cent  of  the  fat  was  removed; 
therefore  the  difference  between  26.19  Per  cent  and 
16.66  per  cent  will  show  what  is  removed  by  skim- 
ming; 26.19 — 16.66=9.53%  removed  by  skimming. 


A  DAIRY   LABORATORY   GUIDE  33 


EXERCISE  V 

BABCOCK  TEST  AND  QUEVENNE 
LACTOMETER 

1.  Test   in   duplicate   by   the    Babcock   method   a 

sample  of  whole  milk  as  follows : 

(a)  Use  ordinary  amount  of  acid. 

(b)  One-half  usual  amount  of  acid. 

(c)  Fill  the  bottle  up  to  the  base  of  the 

neck  with  acid. 

(d)  Use  the  regular  amount  of  acid,  but 

warm  the  acid  and  milk  before  mix- 
ing until  they  feel  warm  to  the  hand. 
Add  the  acid  slowly  to  the  sample. 
Observe  and  record  all  results  care- 
fully. 

Test  for  fat  a  sample  of  butter.  Why  is  it  ad- 
visable to  add  the  acid  slowly  in  (d)  ques- 
tion I? 

2.  (a)     Take  a  Quevenne  lactometer  reading  of  a 

sample    of    whole    milk    and    skimmed 
milk,   making  corrections  for  tempera- 
ture. 
Explain  fully  the  effect  of  temperature  on 

the  lactometer  readings. 

(&)  Starting  with  the  first  reading  in  2  (a), 
what  would  have  been  the  reading  if 
the  temperature  had  been  54°  F.,  62° 
F.,  73°  F.,  81°  F.? 

3.  Add  one-half  an  acid  measure  of  water  to  the 

skimmed  milk  sample  and  take  the  Quevenne 


. 


34  A  DAIRY   LABORATORY   GUIDE 

reading.     Note  any  change  in  the  lactometer 
reading,    and    explain    the    reasons    for    this 
change. 
4.     Take    the    Quevenne    reading    of   a    sample    of 

skimmed  milk. 

Compute  what  the  reading  would  be  if  the  tem- 
perature were  four  degrees  higher.  Verify 
your  results  by  warming  the  sample  and  tak- 
ing the  reading.  Be  sure  to  mix  the  sample 
thoroughly  after  warming  it.  Have  the  tem- 
perature of  the  milk  low  enough  so  that  rais- 
ing the  temperature  four  degrees  will  not 
bring  the  sample  above  70°  F.  Why  should 
not  the  temperature  be  above  70°  F.? 
What  is  the  chief  advantage  of  the  Quevenne 
lactometer  over  other  kinds? 


A  DAIRY  LABORATORY  GUIDE  35 

STUDENT'S  NOTES  AND  REPORT 


36  A  DAIRY   LABORATORY  GUIDE 

STUDENT'S   NOTES   AND    REPORT 


A  DAIRY   LABORATORY   GUIDE  37 

EXPLANATION.     BOARD  OF  HEALTH 
LACTOMETER 

The  Board  of  Health  lactometer  (commonly  called 
B.  of  H.  lactometer)  is  an  instrument  giving1  ar- 
bitrary readings  and  it  must  be  changed  to  equiv- 
alent Quevenne  readings  in  order  to  obtain  the 
specific  gravity.  It  is  of  the  same  general  shape 
as  the  Quevenne,  except  that  the  thermometer 
scale  is  usually  on  the  opposite  side  of  the  stem 
from  the  lactometer  scale.  The  instrument  is 
graduated  from  o  to  120,  and  one  degree  Board  of 
Health  equals  .29  of  one  degree  Quevenne.  In 
order,  therefore,  to  change  from  Board  of 
Health  to  Quevenne,  the  Board  of  Health 
reading  is  multiplied  by  .29.  Vice  versa  to 
change  from  Quevenne  to  Board  of  Health  reading, 
the  Quevenne  reading  is  divided  by  .29.  Like  the 
Quevenne,  the  Board  of  Health  lactometer  is  gradu- 
ated to  be  read  at  a  temperature  of  60°  F.,  and  if 
the  temperature  is  above  or  below  the  standard, 
the  correction  factor  is  .3  of  one  lactometer  degree 
for  every  degree  that  the  sample  is  above  or  below 
the  standard.  The  following  example  will  illustrate 
how  correction  is  made:  B.  of  H.  reading  110.5  at 
65°  F.,  what  would  be  the  reading  at  60°  F.?  The 
sample  must  be  cooled  down  5  degrees;  therefore, 
we  would  add  1.5  (sX-3)  to  tne  reading  (110.5), 
making  a  corrected  reading  of  112.0.  One  of  the 
chief  advantages  of  the  B.  of  H.  lactometer  is  that 
a  small  adulteration  of  the  milk  will  make  a  notice- 
able change  in  the  lactometer  reading.  This  is  be- 
cause the  instrument  has  so  large  a  scale.  Also, 
when  milk  is  watered,  the  number  of  lactometer 
degrees  recorded  below  100  indicates  roughly  the 
per  cent  of  adulteration. 


38  A   DAIRY   LABORATORY   GUIDE 

EXPLANATION.     USE  OF  HAND  MACHINE 
IN  BABCOCK  TEST 

It  is  a  popular  notion  that  milk  cannot  be  tested 
accurately  in  a  hand  machine.  This  is  a  mistaken 
idea,  as  a  hand  machine  should  do  as  good  work  as 
any  other  machine.  One  of  the  chief  reasons  for 
inaccuracy  in  using  a  hand  machine  is  the  inatten- 
tion paid  to  the  temperature.  It  is  necessary  to 
have  the  proper  degree  of  heat  in  order  to  perform 
properly  the  Babcock  test.  To  provide  the  proper 
temperature  the  hand  machine  should  be  filled  with 
hot  water  up  to  the  bottle  cups  if  the  room  is  at  all 
cold.  The  small  two-bottle  and  four-bottle  hand 
testers  have  no  frame,  and  so  the  bottle  cups  are 
made  large  in  order  that  they  may  be  filled  with 
hot  water  if  necessary.  While  it  is  not  absolutely 
necessary  to  use  hot  water  at  all  times,  its  use  is 
always  advisable.  By  its  use  the  danger  of  test- 
ing milk  at  too  cold  a  temperature  is  largely  done 
away  with.  The  operator  should  be  careful  to  keep 
the  machine  to  its  proper  speed  during  the  entire 
run. 


A  DAIRY  LABORATORY  GUIDE  39 


EXERCISE  VI 

BABCOCK  TEST  AND  B.  OF  H. 
LACTOMETER 

1.  Take   the   B.   of  H.   lactometer   reading  of   a 
sample    of    whole    milk.     Remove    the    lactometer, 
measure  out  two  bottles  for  the  Babcock  test  and 
allow  the  milk  to  stand  in  your  lactometer  cylinder 
while  you  do  No.  2.     Then  draw  off  from  the  top 
of  the  sample  all  the  cream  the  pipette  will  hold. 
Then  add  to  the  sample  17.6  cc.  of  water.     Again 
take  a  lactometer  reading  and  make  a  Babcock  test 
and  figure  out  the  per  cent  of  fat  removed  by  skim- 
ming and  the  per  cent  of  fat  removed  by  watering. 
After  drawing  off  cream  and  adding  water  be  sure 
to   mix   the   sample   thoroughly.     Upon   what   rule 
does  your  ability  to  do  the  above  computation  de- 
pend?    Better  results  will  be  obtained  if  the  milk  is 
warmed  to  about  85°   F.  and  allowed  to  stand  as 
long  as  possible.     In  removing  the  cream  keep  the 
point  of  the  pipette  as  near  as  possible  to  the  sur- 
face of  the  liquid. 

2.  Test  in  the  steam  machine  whole  milk,  skim- 
med milk  and  butter.     Run  the  skimmed  milk  ten 
minutes,  two  minutes   and   one  minute.     Use  acid 
one-quarter  inch  above  the  mark.    Retest  the  whole 
milk  in  the' hand  machine  and  compare  the  results 
with  those  obtained  in  the  steam  machine. 

3.  (a)     Take   the   B.   of  H.   lactometer  reading 
of  a  sample  of  skimmed  milk.   See  how  much  water 
it   will   take  to   lower  the   lactometer   reading  one 
degree.     Great  care  must  be  taken  to  mix  the  water 
with  the  milk  as  the  former  is  poured  in.     This  is 


4O  A   DAIRY    LABORATORY    GUIDE 

best  done  by  pouring  the  milk  from  one  vessel  to 
another. 

(b)     See  if  one-half  gram  of  salt  will  bring  the 
reading  back  to  where  it  was  originally. 


A  DAIRY  LABORATORY  GUIDE  4! 

STUDENT'S  NOTES  AND  REPORT 


42  A  DAIRY   LABORATORY   GUIDE 

STUDENT'S   NOTES   AND    REPORT 


A    DAIRY    LABORATORY    GUIDE  43 

EXPLANATION.       ACIDITY  OF  MILK 

The  acidity  of  milk  is  of  two  kinds  —  apparent 
and  real  acidity.  The  apparent  acidity  is  due  to 
the  acid  reaction  of  the  acid  phosphates  and  casein. 
The  real  acidity  is  due  to  the  presence  of  lactic 
acid  (CsHgOa),  which  is  produced  by  the  action  of 
bacteria  upon  the  sugar  of  the  milk.  The  follow- 
ing reaction  is  supposed  to  be  the  one  which  takes 
place: 


The  apparent  acidity,  according  to  Van  Slyke, 
does  not  go  above  .08  per  cent  to  .1  per  cent,  and  is 
of  minor  importance  so  far  as  dairy  work  is  con- 
cerned. In  determining  the  acidity  of  milk  it  is  as- 
sumed that  all  of  the  acidity  is  due  to  the  presence 
of  lactic  acid. 

The  real  acidity  will  ordinarily  go  as  high  as  i 
per  cent,  and  in  some  cases,  higher.  Usually,  how- 
ever, when  from  .8  per  cent  to  I  per  cent  acidity 
is  reached  the  lactic  acid  organisms  will  cease 
working.  If  a  part  of  the  acid  is  neutralized  the 
organisms  will  again  commence  the  production  of 
acid. 

Lactic  acid  is  important  in  the  manufacture  of 
dairy  products.  For  example,  butter  is  churned 
from  cream  which  is  soured  or  "  ripened  "  by  lactic 
acid.  The  presence  and  amount  of  lactic  acid  is 
very  important  all  through  the  process  of  cheese 
making.  In  many  cases  the  nature  of  the  product 
depends  on  the  amount  of  acid  present  during  the 
successive  steps  of  manufacture. 

For  these  reasons  it  is  necessary  to  have  some 
means  of  finding  the  amount  of  acid  in  the  milk. 
The  process  by  which  this  is  done  is  called  titration. 


44  A   DAIRY    LABORATORY    GUIDE 

It  is  a  principle  of  chemistry  that  an  alkali  will 
neutralize  an  acid.  In  order,  therefore,  to  find  the 
acid  in  the  milk  we  take  a  known  quantity  of  the 
milk  and  measure  into  it  an  alkali  whose  strength 
we  know.  The  instrument  used  to  measure  the 
amount  of  alkali  used  is  called  a  burette,  and  the  unit 
of  measure  is  the  cubic  centimeter.  It  is  commonly 
graduated  as  fine  as  tenths  of  a  cubic  cen- 
timeter. One  can  tell  when  all  of  the  acid  is  neu- 
tralized by  means  of  an  indicator.  The  indicator 
used  most  in  dairy  work  is  phenolphthalein,  which  is 
colorless  in  acid  and  pink  in  alkali.  If  two  or  three 
drops  of  the  indicator  are  put  in  milk  the  color  will 
not  change,  because  the  milk  is  acid  in  reaction. 
The  instant  that  just  enough  alkali  is  added  to  the 
milk  to  neutralize  all  of  the  acid  the  solution  will 
turn  pink. 

It  is  a  chemical  fact  that  equal  volumes  of  acids 
and  alkalies  of  the  same  strength  will  exactly  neu- 
tralize one  another.  In  I  cc.  of  a  normal  solution 
of  lactic  acid  there  are  .09  grams  of  lactic  acid. 
According  to  the  above  rule  I  cc.  of  any  normal 
alkali  solution  would  just  neutralize  .09  grams  of 
lactic  acid. 

In  actual  practice  a  solution  weaker  than  a  normal 
solution  is  usually  employed,  because  a  normal  solu- 
tion is  so  strong  that  any  small  variation  in  the 
amount  used  makes  a  big  variation  in  results.  A 
common  solution  used  is  i/io  normal  (expressed 
n/io).  One  cc.  of  an  n/io  alkali  solution  would 
neutralize  .009  grams  of  lactic  acid.  An  example 
will  illustrate  how  the  per  cent  of  acid  in  milk  is 
calculated.  Suppose  it  took  6  cc.  of  n/io  alkali 
solution  to  neutralize  the  acid  in  20  grams  of  milk. 
What  is  the  per  cent  of  acid  ?  One  cc.  of  n/ 10  alkali 
will  neutralize  .009  grams  of  lactic  acid.  Six  cc.  will 


A   DAIRY    LABORATORY   GUIDE  45 

neutralize  6X-OO9=.O54  grams  of  acid.  .054-^-20— 
.0027.  .oo27Xioo=.27%  acid  in  the  milk.  Formu- 
lated, the  above  example  is  expressed  as  follows: 

wjp  x  ioo=.27% 

If  the  milk  for  the  acid  test  is  measured  in  cubic 
centimeters  it  should  be  reduced  to  grams  by  mul- 
tiplying by  the  specific  gravity  of  milk.  The  acid 
is  obtained  in  terms  of  grams  and  we  cannot  divide 
grams  by  cc.  and  obtain  per  cent. 

Professor  Farrington  has  devised  some  alkali 
tablets,  each  one  of  which  will  neutralize  .03492 
grams  of  lactic  acid.  These  tablets  are  dissolved 
in  water  and  an  alkali  solution  made.  The  strength 
of  the  solution  per  cc.  will  vary  according  to  the 
number  of  tablets  used  and  the  number  of  cc.  of 
water  in  which  they  are  dissolved.  The  indicator 
is  added  to  the  tablets  when  they  are  manufactured. 
Consequently,  when  using  an  alkali  tablet  solution 
no  phenolphtholein  is  needed.  A  concrete  example 
will  show  how  these  tablets  are  used. 

Suppose  that  it  required  15  cc.  of  an  alkali  tablet 
solution  to  neutralize  the  acid  in  20  grams  of  milk. 
The  tablet  solution  was  made  by  dissolving  five 
tablets  in  TOO  cc.  of  water.  What  is  the  per  cent 
of  acid  in  the  milk? 

.O3492=grams  of  lactic  acid  one  tablet  will  neu- 
tralize. .03492X5=-  1  746  grams  of  lactic  acid  five 
tablets  will  neutralize.  Since  the  five  tablets  are 
dissolved  in  100  cc.  of  water  .1746  is  the  amount  of 
lactic  acid  100  cc.  of  the  solution  will  neutralize. 
Then  .  1  746-^-  ioo=.oo  1746,  the  strength  of  I  cc.  of 
the  solution  ;  in  other  words,  the  number  of  grams 
of  lactic  acid  i  cc.  of  the  solution  will  neutralize. 


.026i9o-=-20=.ooi  3095  X  i  oo=.  1  3095  % 


46  A  DAIRY   LABORATORY   GUIDE 

If  five  of  the  alkali  tablets  are  dissolved  in  97  cc. 
of  water  each  cubic  centimeter  of  the  solution  will 
neutralize  .01  per  cent  of  acid  when  18  grams  of 
milk  are  used.  This  solution  is  often  used  by 
creamerymen,  as  the  per  cent  of  acid  may  then  be 
read  directly  from  the  burette.  Many  devices  for 
testing-  the  acidity  of  milk  are  on  the  market,  all 
tending-  to  do  away  with  computation  and  giving 
the  percentage  of  acid  directly.  One  of  these  is 
Publow's  acidimeter.  In  this  apparatus  an  n/io 
alkali  solution  is  used  and  9  grams  of  milk  are 
tested.  Each  cc.  on  the  burette  equals  .1  per  cent 
of  acid  and  each  I/TO  of  a  cc.  equals  .01  per  cent 
acid.  In  testing  for  acid  one  should  always  try 
and  obtain  the  same  degree  of  color  each  time. 
This  color  should  be  permanent  for  at  least  one 
minute.  Great  care  should  be  taken  not  to  run  in 
an  excess  of  alkali.  It  will  be  much  easier  to  detect 
the  color  change  if  some  water  is  added  to  the 
sample  after  it  is  measured  out  before  the  alkali 
is  added. 


A   DAIRY    LABORATORY    GUIDE  47 

EXERCISE  VII 
BABCOCK  TEST  AND  ACID  TEST 

1.  (a)   Test  by  the  Babcock  method,  butter,  cream 

and  whole  milk.     Compute  the  weight  of 
the  fat  column  in  the  cream  test. 
(b)   Retest  the  whole  milk,  putting  9  grams  in 
one  bottle  and  5  grams  in  the  other.   Re- 
duce each  reading  to  a  basis  of  18  grams. 

2.  (a)   Test    the    skimmed    milk    for   per   cent    of 

acid,  using  n/io  alkali  solution,  and 
using  18  grams  of  milk. 

(b)  Retest  the  skimmed  milk,  using  25  cc.  of 

milk  and  compare  with  first  test. 

(c)  Measure  out  18  grams  of  skimmed  milk  and 

add  to  this  17.6  cc.  of  water.  Test  for 
acid  and  compare  with  the  first  test. 

(d)  Measure  out  20  cc.  of  skimmed  milk  from 

same  sample  as  used  in  above  experi- 
ments and  add  to  it  3  cc.  of  buttermilk 
or  starter  and  test  for  acid.  What  is 
the  object  of  using  different  amounts  in 
(a)  and  (b)  ?  What  is  the  object  of 
adding  water  to  (c)  ? 

3.  Take   the   B.   of  H.   lactometer  reading  of  the 

whole  milk  and  compute  per  cent  of  T.  S.  and 
S.  N.  F. 

4.  Take   a   lactometer   reading   of   skimmed   milk. 

Cool  the  milk  as  low  as  possible  and  compute 
what  the  reading  would  be  at  this  tempera- 
ture. Then  compare  your  computation  with 
the  actual  reading. 


48  A   DAIRY    LABORATORY    GUIDE 

Perform  the  same  experiment,  heating  the  milk 
to  95°  F.  The  object  of  this  experiment  is 
to  show  the  incorrectness  of  a  correction 
factor  when  used  at  a  temperature  of  more 
than  10°  F.,  either  above  or  below  60°  F. 


A  DAIRY  LABORATORY  GUIDE  49 

STUDENT'S  NOTES  AND  REPORT 


50  A  DAIRY   LABORATORY   GUIDE 

STUDENT'S    NOTES    AND    REPORT 


A  DAIRY  LABORATORY  GUIDE  51 

EXPLANATION.  EFFECT  OF  SPEED  OF 
MACHINE  ON  BABCOCK  TEST 

The  following-  exercise  illustrates  the  influence  of 
the  speed  of  the  machine  on  the  amount  of  fat 
brought  to  the  surface.  The  speed  of  the  machine 
is  important,  because  the  greater  the  speed  the  more 
force  exerted.  One  should  always  run  a  Babcock 
tester  up  to  the  speed  indicated  in  the  directions  for 
running-  the  machine.  Sometimes  one  will  make  as 
good  a  test  when  running  a  machine  slow  as  when 
running  faster.  This,  however,  is  not  always  the 
case,  and  in  operating  the  tester  one  must  be  sure 
that  the  machine  is  run  fast  enough  to  bring  all  of 
the  fat  into  the  neck  of  the  bottle. 


52  A  DAIRY   LABORATORY   GUIDE 

*• 

EXERCISE  VIII 
BABCOCK   TEST   AND    LACTOMETER 

1.  (a]   Test  by  the  Babcock  method  a  sample  of 

whole  milk,  skimmed  milk  and  butter. 

(&)   Retest  the  butter  in  the  hand  machine. 

(c)  Retest  the  whole  milk  in  the  steam  ma- 
chine, but  do  not  let  the  speed  of  the 
machine  exceed  250  revolutions  per 
minute. 

In  performing  the  above  experiment  it  is 
best  to  experiment  with  the  machine 
before  putting  in  your  samples.  Other- 
wise, you  will  be  liable  to  run  the  ma- 
chine too  fast. 

2.  (a)   Take    a   lactometer   reading   of   the   whole 

milk  and  figure  out  the  S.  N.  F.  and 
T.  S. 

(&)  Take  a  lactometer  reading  of  the  skimmed 
milk  and  figure  out  the  S.  N.  F.  and  T.  S. 

3.  (a)   Test  the  skimmed  milk  for  acid  with  n/io 

alkali  solution  and  the  alkali  tablet  solu- 
tion. The  alkali  tablet  solution  was 
made  by  dissolving  eight  tablets  in  95  cc. 
of  water. 

(b)  Test  for  acid  18  grams  of  tap  water.  Add 
to  18  grams  of  tap  water  3  cc.  of  starter 
or  buttermilk,  again  test  for  acid.  Use 
n/io  alkali  solution. 


A  DAIRY  LABORATORY  GUIDE  53 

STUDENT'S  NOTES  AND  REPORT 


54          A  DAIRY  LABORATORY  GUIDE 

STUDENT'S  NOTES  AND  REPORT 


A   DAIRY    LABORATORY    GUIDE  55 


EXERCISE  IX 

BABCOCK  TEST.     LACTOMETER  READING 
AND    ACID    TEST 

1.  Make  a  Babcock  test  of  cheese,  whole  milk  and 

skimmed  milk.  Add  acid  to  the  skimmed 
milk  about  one-quarter  of  an  inch  above  the 
usual  mark,  and  run  ten  minutes,  two  min- 
utes and  one  minute. 

Run  the  whole  milk  the  usual  time  at  the  usual 
speed.  Be  sure  to  cut  the  cheese  fine  before 
putting  into  the  test  bottle. 

2.  (a)   Retest  the  whole  milk,  running  the  machine 

one  minute,  one  minute,  one  minute.  Do 
you  get  any  different  results  either  in  the 
amount  or  the  appearance  of  fat?  If  so, 
give  the  reasons. 

(b)  Retest  the  whole  milk,  running  the  machine 
fifteen  minutes,  five  minutes  and  three 
minutes.  Do  you  get  any  more  fat  than 
when  the  machine  is  run  the  usual  length 
of  time? 
Oil  the  machine  well  before  each  run. 

3.  Take    the     B.    of    H.     lactometer    reading    of 

skimmed  milk  and  whole  milk.  Make  correc- 
tions for  temperature  and  figure  out  the 
S.  N.  F.  and  T.  S.  For  whole  milk  use  three 
formulae. 

4.  Test  the  whole  milk  for  acid,  using  18  grams. 

Use  both  n/io  and  alkali  tablet  solution. 
Test  the  skimmed  milk  for  acid,  with  the  n/io 
solution.  Use  only  5  cc.  of  the  milk,  so  that 
one  result  will  be  a  check  on  the  other. 


56  A   DAIRY    LABORATORY    GUIDE 

Again  test  the  skimmed  milk,  using  a  5o-cc. 
sample.  Do  this  twice'.  See  if  you  get  the 
more  uniform  results  with  the  large  sample. 


A  DAIRY  LABORATORY  GUIDE  57 

STUDENT'S  NOTES  AND  REPORT 


58  A  DAIRY   LABORATORY  GUIDE 

STUDENT'S   NOTES   AND    REPORT 


A   DAIRY    LABORATORY    GUIDE..  59 

EXERCISE  X 
BABCOCK    TEST    AND    ACID    TEST 

Make  up  an  alkali  tablet  solution  as  directed. 
Shake  frequently,  and  set  aside  for  use  later 
in  the  exercise. 

(a)  Test  by  the  Babcock  method  a  sample  of 

whole  milk  and  a  sample  of  butter. 

(b)  Place  a  piece  of  butter  in  your  acid  measure 

and  allow  it  to  stand  in  a  cup  of  hot 
water  for  about  fifteen  minutes.  Then 
with  a  pipette  draw  the  fat  from  the  sur- 
face of  the  liquid,  and  test  by  the  Bab- 
cock  method.  What  conclusions  do  you 
draw  from  this  experiment? 

Test  for  acid  a  sample  of  starter,  using  the 
alkali  tablet  solution  furnished  and  n/io 
alkali  solution. 

Pour  back  and  forth  from  one  vessel  to  another 
about  100  cc.  of  skimmed  milk.  Do  this  for 
about  three  minutes.  Test  25  cc.  of  it  for 
acid,  using  the  alkali  tablet  solution  which 
you  made  up  at  the  beginning  of  the  exer- 
cise. Then  boil  about  35  cc.  of  the  milk  for 
about  one  minute ;  cool ;  keep  covered  while 
cooling,  and  retest  25  cc.  for  acid.  Compare 
with  first  test  and  see  if  you  get  lower 
results. 

Explain  fully  why  lower  results  may  be  ex- 
pected with  boiled  milk. 

The  alkali  tablet  solution  was  made  by  dissolv- 
ing 10  alkali  tablets  in  115  cc.  of  water. 


60  A  DAIRY  LABORATORY  GUIDE 

STUDENT'S  NOTES  AND  REPORT 


A  DAIRY  LABORATORY  GUIDE          6l 

STUDENT'S  NOTES  AND  REPORT 


62  A   DAIRY    LABORATORY    GUIDE 

EXPLANATION  OF  EXERCISE  X 

In  testing  butter  by  the  Babcock  method,  the 
practice  is  sometimes  followed  of  melting  the 
butter  and  then  putting  it  into  the  test  bottle 
by  means  of  the  pipette.  It  is  possible  to  do 
this  sometimes  and  get  accurate  results,  but 
the  tendency  for  fat  and  water  to  separate 
makes  it  difficult  to  get  accurate  tests. 

Division&of  experiment  2  illustrates  how  readily 
the  fat  and  water  separate.  In  drawing  off 
the  fat  for  this  experiment,  keep  the  point  of 
the  pipette  at  the  surface  of  the  fat. 

Carbon  dioxide  acts  toward  an  alkali  like  an 
acid.  We  are  told  that  some  of  the  acidity 
of  the  milk  is  due  to  the  presence  of  CC>2. 
In  experiment  4,  pouring  the  milk  back  and 
forth  from  one  vessel  to  another  tends  to  mix 
the  CC>2  of  the  air  with  the  milk.  Heat  will 
expel  the  CO2,  and  so  after  boiling  the  milk 
the  acid  test  would  be  lower  than  it  would 
be  before  boiling.  This  experiment  also 
shows  that  milk  will  take  up  gases. 


A  DAIRY   LABORATORY   GUIDE  63 


EXERCISE  XI 

BABCOCK  TEST  AND  BUTTER  MOISTURE 
TEST 

1.  Test    a    sample    of    cheese,    whole    milk    and 

skimmed  milk  for  butter  fat.  In  testing  the 
skimmed  milk,  run  extra  time  and  use  extra 
acid  as  previously  directed. 

2.  Test   cheese   for  acid,   using   n/io   alkali   solu- 

tion. In  order  to  test  cheese  for  acid,  weigh 
out  3  grams.  Place  in  a  white  cup  and  add 
17.6  cc.  of  warm  water.  Then  with  a  stirring 
rod  grind  the  cheese  up  as  fine  as  possible. 
This  will  take  at  least  five  minutes.  Then 
test  the  solution  as  usual,  and  calculate  the 
per  cent  of  acid. 

3.  Test  a  sample  of  butter  for   moisture  by  the 

C.  U.  method. 

NOTE. — To    what    is    the  high    acid    content    of 
cheese  due? 


64  A  DAIRY   LABORATORY   GUIDE 

STUDENT'S   NOTES   AND    REPORT 


A  DAIRY   LABORATORY   GUIDE  65 

STUDENT'S   NOTES   AND    REPORT 


66  A  DAIRY   LABORATORY   GUIDE 


EXERCISE    XII 

BABCOCK  TEST,  LACTOMETER  AND  ACID 
TEST 

1.  Test  by  the  Babcock  method  a  sample  of  whole 

milk,  cottage  cheese  and  buttermilk.  Fill 
your  lightning  top  sample  jar  about  one-third 
full  of  whole  milk,  add  a  preservative  tablet 
and  shake  at  intervals  until  tablet  is  dis- 
solved. Set  the  sample  away  in  your  desk 
and  test  at  the  next  exercise. 
Use  9  grams  of  cottage  cheese,  and  add  9  grams 
of  water.  Test  in  whole  milk  bottle.  Shake 
well  after  adding  acid. 

2.  To  about  54  grams  of  skimmed  milk  add  2  cc. 

of  light  machine  oil,  shake  thoroughly  and 
test  in  duplicate  by  the  Babcock  method. 
Compare  the  appearance  of  the  fat  column 
with  that  obtained  with  ordinary  butter. 

3.  Test  with  the  alkali  tablet  solution  the  acid  in 

the  whole  milk  and  buttermilk. 

4.  Take  a  lactometer  reading  of  the  whole  milk. 

Add  some  water  (about  25  cc.)  to  the 
sample.  Again  take  a  lactometer  reading 
and  make  a  Babcock  test.  Figure  out  T.  S. 
and  S.  N.  F.  and  the  per  cent  of  the  water 
added. 


A  DAIRY  LABORATORY  GUIDE  67 

STUDENT'S  NOTES  AND  REPORT 


68  A  DAIRY   LABORATORY  GUIDE 

STUDENT'S   NOTES   AND    REPORT 


A   DAIRY    LABORATORY    GUIDE  69 

EXPLANATION.     COMMERCIAL  RENNET 
AND  ITS  USE 

Commercial  rennet  is  a  liquid  prepared  by  soak- 
ing in  brine  the  fourth  stomach  of  the  calf.  It  has 
under  certain  conditions  the  power  of  precipitating 
the  casein  from  milk.  It  is  so  desirable  for  this 
purpose  that  rennet  is  used  almost  exclusively  in 
the  manufacture  of  cheese.  One  peculiar  character- 
istic of  rennet  is  the  fact  that  it  is  not  destroyed 
by  its  use  in  precipitating  casein.  If  it  could  be 
extracted  the  same  rennet  could  be  used  over  and 
over  again  for  precipitating  the  casein  in  different 
lots  of  milk. 

Temperature  has  a  decided  effect  upon  the  action 
of  rennet.  The  colder  milk  is,  the  less  rapid  the 
rennet  action.  This  is  very  noticeable  at  tempera- 
tures below  80°  F.  The  rennet  acts  most  rapidly 
at  temperatures  from  100°  F.  to  120°  F.  At  130° 
F.  the  action  of  the  rennet  is  less  active  and  its 
action  is  entirely  destroyed  somewhere  between 
140°  F.  and  150°  F.  The  high  temperature  destroys 
the  rennin,  which  is  the  active  principle  of  the 
rennet.  The  action  of  rennet  increases  as  the  acid 
in  the  milk  increases.  The  action  of  rennet  seems 
to  depend  .to  a  great  degree  upon  the  solubility  of 
the  lime  salts  of  the  milk.  If  an  insoluble  lime 
salt  is  added  to  the  milk,  the  action  of  the  rennet 
is  retarded,  and  if  a  soluble  lime  salt  is  added  to 
milk  the  action  of  rennet  is  hastened.  If  milk  is 
heated  to  a  high  temperature  the  lime  salts  are 
supposed  to  be  rendered  insoluble  and  the  rennet 
has  no  effect  on  the  casein.  Freezing  does  not  seem 
to  injure  rennet.  When  it  is  again  melted  and 
given  the  proper  temperature  it  will  act  as  though 
it  had  never  been  frozen. 


7O  A  DAIRY    LABORATORY    GUIDE 


EXERCISE  XIII 

BABCOCK    TEST,    MICROSCOPIC    APPEAR- 
ANCE OF  MILK,  USE  OF  RENNET 

1.  Test  the  composite  sample  preserved  at  the  last 

exercise. 

2.  Examine     under     the     high-power     microscope 

cream,  whole  milk  and  skimmed  milk.  Make 
a  drawing  of  each  field.  Describe  fully  the 
difference  in  the  appearance  of  the  fat 
globules  in  each  of  the  three  fields. 

3.  Heat  18  grams  of  skimmed  milk  to  about  100° 

F.  and  add  four  drops  of  rennet ;  shake  thor- 
oughly and  let  stand.  Note  the  length  of 
time  it  takes  the  milk  to  curdle. 

4.  To  one-half  a  teacup  of  water  add  six  drops  of 

sulphuric  acid.  Add  three  drops  of  this  solu- 
tion to  18  grams  of  milk.  Heat  to  about 
100°  F.  and  add  four  drops  of  rennet  and 
note  the  time  it  takes  for  milk  to  coagulate. 
Compare  length  of  time  with  that  required 
in  No.  3. 

5.  To  about  20  grams  of  skimmed  milk  add  six 

drops  of  sulphuric  acid  and  shake  thoroughly. 
Note  time  it  takes  the  milk  to  coagulate  and 
compare  the  coagulum  with  that  obtained 
when  rennet  is  used. 

6.  Measure   out   two   25   cc.   samples   of  skimmed 

milk.  Warm  to  80°  F.  To  one  sample  add 
five  drops  of  rennet ;  to  the  other  add  five 
drops  of  sulphuric  acid.  Note  and  compare 
the  length  of  time  it  takes  each  to  coagulate. 


A  DAIRY  LABORATORY  GUIDE 

STUDENT'S  NOTES  AND  REPORT 


72  A   DAIRY   LABORATORY   GUIDE 

STUDENT'S    NOTES    AND    REPORT 


A   DAIRY    LABORATORY   GUIDE  73 

EXERCISE  XIV 
BABCOCK  TEST  AND  USE  OF  RENNET 

1.  Test  by  the  Babcock  method  a  sample  of  butter- 

milk and  a  sample  of  skimmed  milk  cheese 
and  whole  milk  cheese.  Compare  the  results 
of  the  cheese  tests. 

2.  Boil  a  sample  of  milk  for  about  two  minutes  and 

then  cool.  Add  some  rennet  and  see  if  the 
milk  will  coagulate. 

3.  Boil  25  cc.  of  milk  for  about  two  minutes  and 

then  cool.  Add  one-half  cc.  of  sulphuric  acid 
and  see  if  the  milk  will  coagulate. 

4.  Add  to  25  cc.  of  milk  six  drops  of  rennet.     Have 

the  temperature  of  the  milk  at  100°  F.  Note 
the  time  it  takes  the  milk  to  coagulate.  Test 
25  cc.  of  the  same  lot  of  milk  for  acid.  Com- 
pute the  amount  of  n/io  alkali  necessary  to 
neutralize  the  acid  in  50  grams  of  the  milk. 
Divide  the  milk  into  two  portions  of  25  cc. 
each  and  bring  the  temperature  of  each  to 
100°  F.  and  add  to  each  six  drops  of  rennet. 
Note  the  time  it  takes  the  samples  to  co- 
agulate. Compare  with  the  length  of  time 
required  to  coagulate  the  milk  before  the 
alkali  was  added. 


Y) 


74  A   DAIRY   LABORATORY   GUIDE 

STUDENT'S    NOTES    AND    REPORT 


A  DAIRY  LABORATORY  GUIDE 

STUDENT'S  NOTES  AND  REPORT 


76 


A   DAIRY    LABORATORY    GUIDE 


2. 


EXERCISE  XV 

BABCOCK  TEST  AND  LACTOMETER 
READING 

Take  a  lactometer  reading  and  make  a  Babcock 
test  of  a  sample  of  whole  milk.  Compute  the 
T.  S.  and  the  S.  N.  F.  Allow  the  sample  to 
stand  in  the  lactometer  cylinder  while  you 
do  No.  2.  Then  remove  all  of  the  cream  pos- 
sible and  add  25  cc.  of  water.  A^ain  make 
a  Babcock  test,  and  take  a  lactometer  read- 
ing. Compute  the  per  cent  of  water  added, 
the  rate  per  cent  at  which  water  was  added, 
the  per  cent  of  fat  removed  by  skimming, 
the  per  cent  of  fat  removed  bv  watering  and 
the  rate  per  cent  at  which  the  fat  was  re- 
moved. 

Test  in  the  steam  machine  a  sample  of  whole 
milk,  and  a  sample  of  butter.  Retest  a 
sample  from  the  same  lot  of  milk  in 
the  hand  machine  and  fill  the  machine 
with  water  at  60°  F.  Note  the  result 
of  the  low  temperature  upon  the  fat  column. 
Run  the  same  bottles  Avhich  were  tested  in 
the  hand  machine  in  the  steam  machine  for 
a  period  of  three  minutes  and  then  read  the 
fat  column.  Note  if  there  is  any  increase 
in  the  fat  column. 


A  DAIRY  LABORATORY  GUIDE  77 

STUDENT'S  NOTES  AND  REPORT 


78  A  DAIRY   LABORATORY   GUIDE 

STUDENT'S   NOTES   AND    REPORT 


A   DAIRY   LABORATORY   GUIDE  79 


EXERCISE  XVI 

USE  OF  RENNET.    PRECIPITATION  OF 
ALBUMEN 

1.  Take  18  grams  of  milk  in  a  white  cup  and  cool  to 

50°  F.  Add  four  drops  of  rennet  and  note 
time  it  takes  the  milk  to  coagulate.  Com- 
pare this  with  the  same  amount  of  milk 
warmed  to  85°  F.,  to  which  four  drops  of 
rennet  have  been  added. 

2.  Boil  some  whey  and  note  the  albumen  which  is 

thrown  ^down  in  a  white  flocculent  pre- 
cipitate. Fill  your  lightning  top  sample  jar 
about  one-half  full  of  skimmed  milk  at  about 
100°  F.  Add  i  cc.  of  rennet.  Set  aside  to 
coagulate.  Then  strain  off  the  whey  and 
precipitate  the  albumen  in  the  whey  by  boil- 
ing. 

In  both  cases  the  boiling  should  be  done  in  a 
test  tube.  It  may  at  first  be  difficult  to  see 
albumen,  as  it  is  in  very  fine  particles.  The 
albumen  may  be  distinguished  more  readily 
by  holding  the  test  tube  between  the  eye  and 
the  window. 

Turn  in  desk,  key  and  locker.  See  that  all  glass- 
ware is  clean  before  turning  in  the  desk. 


8O  A  DAIRY  LABORATORY  GUIDE 

STUDENT'S  NOTES  AND  REPORT 


A  DAIRY  LABORATORY  GUIDE  8 1 

STUDENT'S  NOTES  AND  REPORT 


INDEX 


PAGE 

Acid: 

Lactic  43 

Measure    5 

In  Milk   43 

Sulphuric 5 

Acidity : 

Apparent  and  real 43 

As  effected  by  CO, 62 

Alkali  Tablet  Solution 45 

Babcock  Test 5 

Boiled  Milk  Test 18 

Burette 44 

Butter  Fat 2 

Melting  point    3 

Moisture  in 19 

Preparation  for  fat  test 19 

Preparation  for  moisture  test 23 

Casein 3 

Amount  in  milk   3 

Characteristics  of    3 

Commercial    uses    of 3 

Collodial   state    3 

Cornell  Moisture  Test 23 

Cream 7 

Viscosity  of   7 

Weighing  for  testing 7 

Fat 1 

Composition  of  3 

Formaldehyde  Test 18 

Galactase 18 

Indicator  44 

Lactometer  27 

Board  of  Health 37 

Quevenne    27 

Uses  of   29 

Machines    6 

Hand 38 

Effect  of  speed  on  test 51 

Melting  Point  of  Butter  Fat 3 


84  DAIRY    LABORATORY    GUIDE 

PAGE 

Milk    1 

Adulteration     31 

Albumen  in    4 

Ash  in 4 

Composition  of  1 

Casein  in 3 

Fat  in 2 

Sugar  in   4 

Water  in 1 

Phenolphthalein    44 

Pipette 5 

Reading  Fat  Column   6 

Rennet   69 

Effect  of  acid  on  action 69 

Effect  of  temperature  on  action 69 

Solids  Not  Fat. 29 

Formulae  for  finding 29 

Specific  Gravity 27 

Of  milk  27 

Testing : 

Butter 8 

Cheese    8 

Cream    7 

Skimmed  milk  7 

Whey   9 

Whole  milk 5 

Temperature : 

Effect  on  lactometer  reading 28 

Effect  on  fat  column 6 

Effect  on  rennet  action 69 


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regular  sequence  of  thought  from  the  beginning  to  the  end 
of  the  book.  The  book  is  intended  to  meet  the  needs  of  all 
persons  interested  in  the  breeding  and  rearing  of  live  stock. 
Illustrated.  405  pages.  5x7  inches.  Cloth.  .  .  .  $1.50 

Forage  Crops  Other  Than  Grasses 

By  THOMAS  SHAW.  How  to  cultivate,  harvest  and  use 
them.  Indian  corn,  sorghum,  clover,  leguminous  plants,  crops 
of  the  brassica  genus,  the  cereals,  millet,  field  roots,  etc. 
Intensely  practical  and  reliable.  Illustrated.  287  pages.  5x7 
inches.  Cloth $1.00 

Soiling  Crops  and  the  Silo 

By  THOMAS  SHAW.  The  growing  and  feeding  of  all  kinds 
of  soiling  crops,  conditions  to  which  they  are  adapted,  their 
plan  in  the  rotation,  etc.  Not  a  line  is  repeated  from  the 
Forage  Crops  book.  Best  methods  of  building  the  silo,  filling 
it  and  feeding  ensilage.  Illustrated.  364  pages.  5x7  inches. 
Cloth $1.50 

The  Study  of  Breeds 

By  THOMAS  SHAW.  Origin,  history,  distribution,  charac- 
teristics, adaptability,  uses,  and  standards  of  excellence  of  all 
pedigreed  breeds  of  cattle,  sheep  and  swine  in  America.  The 
accepted  text  book  in  colleges,  and  the  authority  for 
farmers  and  breeders.  Illustrated.  371  pages.  5x7  inches. 
Cloth $1.50 

Clovers  and  How  to  Grow  Them 

By  THOMAS  SHAW.  This  is  the  first  book  published  which 
treats  on  the  growth,  cultivation  and  treatment  of  clovers  as 
applicable  to  all  parts  of  the  United  States  and  Canada,  and 
which  takes  up  the  entire  subject  in  a  systematic  way  and 
consecutive  sequence.  The  importance  of  clover  in  the  econ- 
omy of  the  farm  is  so  great  that  an  exhaustive  work  on  this 
subject  will  no  doubt  be  welcomed  by  students  in  agriculture, 
as  well  as  by  all  who  are  interested  in  the  tilling  of  the  soil. 
Illustrated.  5x7  inches.  337  pages.  Cloth.  Net  .  .  $1.00 

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